This invention relates to permanent magnet dynamo electric machines and more specifically to permanent magnet dynamo electric machines with the premanent magnets located in the interior of the rotor.
Alternating current electric motors and generators are sometimes excited or magnetized by means of permanent magnets because this leads to machines of simple, robust construction having high efficiency and being free of slip rings or commutators.
There is a need for adequate mechanical support of the permanent magnets situtated in the interior of the rotor of a permanent magnet machine. The magnets, as well as the surrounding structures are subject to various systems of forces arising from thermal expansion, rotation and residual forces caused by the manufacturing process, such as distortion due to welding. The magnet material is often Alnico, ferrite, rare earth-cobalt, or manganese-aluminum. Most of these materials are hard to machine, and therefore it is economically desirable to be able to assemble magnets that have irregular surfaces rather than close tolerance ground surfaces. Many of the useful magnet materials are quite brittle. It is necessary to mount such magnets in laminated rotor structures in a way that will resist loosening due to vibration, centrifugal forces, temperature excursions and be compatible with mass production techniques.
In previous permanent magnet rotor designs, such as the one shown in Richter's U.S. Pat. No. 4,117,360, issued Sept. 26, 1978, and assigned to the instant assignee, a composite shrink ring of magnetic and nonmagnetic pieces welded together is used to hold the magnet and the remaining rotor assembly. The pole pieces and rotor assembly are solid pieces of magnetic material.
In the copending application of Miller et al., Ser. No. 315,333, filed Oct. 26, 1981, now U.S. Pat. No. 4,417,168 and assigned to the instant assignee, a prism of magnetic material separated along a plane parallel to a flux line has a planar spring disposed between the sections to force the "V" arranged magnets against the pole pieces.
In the copending application of Miller et al., Ser. No. 453,665, filed Dec. 27, 1982, and assigned to the instant assignee, north and south pole pieces are separated by clamp pieces to form a hollow cylinder. A shaft of magnetic material with a central portion of rhombic cross section is positioned in the cylinder. As bolts extending through the clamp pieces engage matching surfaces on the edges of the pole pieces, the pole pieces are drawn toward the shaft, and in doing so clamp the magnets located adjacent the sides of the magnet in compression to form a solid structure.
In the copending application of Miller et al., Ser. No. 453,666, filed Dec. 27, 1982, and assigned to the instant assignee a permanent magnet rotor has a north and south pole piece, each separated into two sections by a central nonmagnetic insert. The pole piece sections are welded to the central nonmagnetic insert, and two nonmagnetic segments are welded to either end of the south pole piece to form two half rings. The half rings are secured about a solid shaft of magnetic material having a central portion with a rhombic cross section. The central line of the half rings is aligned with the diagonal of the rhombic central portion. The half rings are bolted to one another. The sides of the shaft and the inner faces of the half rings form four apertures extending the axial length of the pole pieces. A magnet which adds no structural strength to the rotor is positioned in each of the apertures, respectively.
It is an object of the present invention to provide a rotor for a permanent magnet machine which can be fabricated by standard manufacturing processes such as punching and pressing and requires a minimum of machining.
It is another object of the present invention to provide a rotor which allows easy insertion of magnets in their respective slots and subsequently adjusts each lamination to the local tolerance of the magnet thickness.
It is a further object of the present invention to provide a rotor for a permanent magnet machine that does not require bolts extending in the radial direction to provide radial tightening.